What are secondary sugars? I'm studying for the final tomorrow and we are focusing a lot on the lac operon series and some of the metabolic processes of sugars. I know that bacteria cells prefer galactose, but will still use lactose, so does that mean lactose is a secondary sugar? Also does that make allolactose(lac operon inducer) a secondary sugar?

Not sure why I can't edit the above part, but I stumbled across something that seemed to be of use; that secondary sugars might be sugars the require cAMP and CRP to be the effector of the operon(along with the operon inducer of course). Since gallactose is what the cell wants the most then the other metabolic operons(like lactose) should be off so any sugar that isn't gallactose is secondary?

If I understand correctly, primary sugars are metabolised primarily, i.e. with no induction but also their metabolism is not inhibited. On the other hand the metabolic enzymes of secondory sugars must be induced first.